Use of functional proteomics to investigate PKC epsilon-mediated cardioprotection: the signaling module hypothesis

Privileged scaffolds as MAO inhibitors: Retrospect and prospects

This review aims to be a comprehensive, authoritative, critical, and readable review of general interest to the medicinal chemistry community because it focuses on the pharmacological, chemical, structural and computational aspects of diverse chemical categories as monoamine oxidase inhibitors (MAOIs). Monoamine oxidases (MAOs), namely MAO-A and MAO-B represent an enormously valuable class of neuronal enzymes embodying neurobiological origin and functions, serving as potential therapeutic target in neuronal pharmacotherapy, and hence we have coined the term "Neurozymes" which is being introduced for the first time ever. Nowadays, therapeutic attention on MAOIs engrosses two imperative categories; MAO-A inhibitors, in certain mental disorders such as depression and anxiety, and MAO-B inhibitors, in neurodegenerative disorders like Alzheimer's disease (AD) and Parkinson's disease (PD). The use of MAOIs declined due to some potential side effects, food and drug interactions, and introduction of other classes of drugs. However, curiosity in MAOIs is reviving and the recent developments of new generation of highly selective and reversible MAOIs, have renewed the therapeutic prospective of these compounds. The initial section of the review emphasizes on the detailed classification, structural and binding characteristics, therapeutic potential, current status and future challenges of the privileged pharmacophores. However, the chemical prospective of privileged scaffolds such as; aliphatic and aromatic amines, amides, hydrazines, azoles, diazoles, tetrazoles, indoles, azines, diazines, xanthenes, tricyclics, benzopyrones, and more interestingly natural products, along with their conclusive SARs have been discussed in the later segment of review. The last segment of the article encompasses some patents granted in the field of MAOIs, in a simplistic way.

Undiscovered Physiology of Transcript and Protein Networks

The past two decades have witnessed a rapid evolution in our ability to measure RNA and protein from biological systems. As a result, new principles have arisen regarding how information is processed in cells, how decisions are made, and the role of networks in biology. This essay examines this technological evolution, reviewing (and critiquing) the conceptual framework that has emerged to explain how RNA and protein networks control cellular function. We identify how future investigations into transcriptomes, proteomes, and other cellular networks will enable development of more robust, quantitative models of cellular behavior whilst also providing new avenues to use knowledge of biological networks to improve human health. © 2016 American Physiological Society. Compr Physiol 6:1851-1872, 2016.

PKCε inhibits isolation and stemness of side population cells via the suppression of ABCB1 transporter and PI3K/Akt, MAPK/ERK signaling in renal cell carcinoma cell line 769P

Protein kinase C epsilon (PKCε), a member of the novel PKC family, is known to be a transforming oncogene and tumor biomarker for many human solid cancers including renal cell carcinoma (RCC). We isolated side population (SP) cells from the RCC 769P cell line, and proved that those cells possess cancer stem cell (CSC) characteristics. In this study, to identify the function of PKCε in cancer stemness of 769P SP cells, we reduced the expression of PKCε in those cells, following the results demonstrated that PKCε depletion had a negative correlation with the existence of SP cells in 769P cell line. Down-regulation of PKCε also suppresses the CSC potential of sorted 769P SP cells in several ways: proliferation potential, resistance to chemotherapeutics and in vivo tumor formation ability. Our study also reveals that PKCε is associated with ABCB1 and this association probably contributed to the SP cells isolation from 769P cell line. Furthermore, the expression of ABCB1 is directly regulated by PKCε. Additionally, after the depletion of PKCε, the phosphorylation of pAkt, pStat3 and pERK was apparently suppressed in 769P SP cells, whereas PKCε overexpression could promote the phosphorylation of AKT, STAT3 and ERK in 769P Non-SP cells. Overall, PKCε down-regulation suppresses sorting and the cancer stem-like phenotype of RCC 769P SP cells through the regulation of ABCB1 transporter and the PI3K/Akt, Stat3 and MAPK/ERK pathways that are dependent on the phosphorylation effects. Thus, PKCε may work as an important mediator in cancer stem cell pathogenesis of renal cell cancer.

The Multifunctional Protein Kinase C-ε in Cancer Development and Progression

The protein kinase C (PKC) family proteins are important signal transducers and have long been the focus of cancer research. PKCɛ, a member of this family, is overexpressed in most solid tumors and plays critical roles in different processes that lead to cancer development. Studies using cell lines and animal models demonstrated the transforming potential of PKCɛ. While earlier research established the survival functions of PKCɛ, recent studies revealed its role in cell migration, invasion and cancer metastasis. PKCɛ has also been implicated in epithelial to mesenchymal transition (EMT), which may be the underlying mechanism by which it contributes to cell motility. In addition, PKCɛ affects cell-extracellular matrix (ECM) interactions by direct regulation of the cytoskeletal elements. Recent studies have also linked PKCɛ signaling to cancer stem cell functioning. This review focuses on the role of PKCɛ in different processes that lead to cancer development and progression. We also discussed current literatures on the pursuit of PKCɛ as a target for cancer therapy.

Targeting aldehyde dehydrogenase 2: new therapeutic opportunities

A family of detoxifying enzymes called aldehyde dehydrogenases (ALDHs) has been a subject of recent interest, as its role in detoxifying aldehydes that accumulate through metabolism and to which we are exposed from the environment has been elucidated. Although the human genome has 19 ALDH genes, one ALDH emerges as a particularly important enzyme in a variety of human pathologies. This ALDH, ALDH2, is located in the mitochondrial matrix with much known about its role in ethanol metabolism. Less known is a new body of research to be discussed in this review, suggesting that ALDH2 dysfunction may contribute to a variety of human diseases including cardiovascular diseases, diabetes, neurodegenerative diseases, stroke, and cancer. Recent studies suggest that ALDH2 dysfunction is also associated with Fanconi anemia, pain, osteoporosis, and the process of aging. Furthermore, an ALDH2 inactivating mutation (termed ALDH2*2) is the most common single point mutation in humans, and epidemiological studies suggest a correlation between this inactivating mutation and increased propensity for common human pathologies. These data together with studies in animal models and the use of new pharmacological tools that activate ALDH2 depict a new picture related to ALDH2 as a critical health-promoting enzyme.

mTOR complex 2 mediates Akt phosphorylation that requires PKCε in adult cardiac muscle cells

Our earlier work showed that mammalian target of rapamycin (mTOR) is essential to the development of various hypertrophic responses, including cardiomyocyte survival. mTOR forms two independent complexes, mTORC1 and mTORC2, by associating with common and distinct cellular proteins. Both complexes are sensitive to a pharmacological inhibitor, torin1, although only mTORC1 is inhibited by rapamycin. Since mTORC2 is known to mediate the activation of a prosurvival kinase, Akt, we analyzed whether mTORC2 directly mediates Akt activation or whether it requires the participation of another prosurvival kinase, PKCε (epsilon isoform of protein kinase-C). Our studies reveal that treatment of adult feline cardiomyocytes in vitro with insulin results in Akt phosphorylation at S473 for its activation which could be augmented with rapamycin but blocked by torin1. Silencing the expression of Rictor (rapamycin-insensitive companion of mTOR), an mTORC2 component, with a sh-RNA in cardiomyocytes lowers both insulin-stimulated Akt and PKCε phosphorylation. Furthermore, phosphorylation of PKCε and Akt at the critical S729 and S473 sites respectively was blocked by torin1 or Rictor knockdown but not by rapamycin, indicating that the phosphorylation at these specific sites occurs downstream of mTORC2. Additionally, expression of DN-PKCε significantly lowered the insulin-stimulated Akt S473 phosphorylation, indicating an upstream role for PKCε in the Akt activation. Biochemical analyses also revealed that PKCε was part of Rictor but not Raptor (a binding partner and component of mTORC1). Together, these studies demonstrate that mTORC2 mediates prosurvival signaling in adult cardiomyocytes where PKCε functions downstream of mTORC2 leading to Akt activation.

Structural considerations for chromatin state models with transcription as a functional readout

Lacking from the rapidly evolving field of chromatin regulation is a discrete model of chromatin states. We propose that each state in such a model should meet two conditions: a structural component and a quantifiable effect on transcription. The practical benefits to the field of a model with greater than two states (including one with six states, as described herein) would be to improve interpretation of data from disparate organ systems, to reflect temporal and developmental dynamics and to integrate the, at present, conceptually and experimentally disparate analyses of individual genetic loci (in vitro or using single gene approaches) and genome-wide features (including ChlP-seq, chromosomal capture and mRNA expression via microarrays/sequencing).

Genomes, proteomes, and the central dogma

Systems biology, with its associated technologies of proteomics, genomics, and metabolomics, is driving the evolution of our understanding of cardiovascular physiology. Rather than studying individual molecules or even single reactions, a systems approach allows integration of orthogonal data sets from distinct tiers of biological data, including gene, RNA, protein, metabolite, and other component networks. Together these networks give rise to emergent properties of cellular function, and it is their reprogramming that causes disease. We present 5 observations regarding how systems biology is guiding a revisiting of the central dogma: (1) It deemphasizes the unidirectional flow of information from genes to proteins; (2) it reveals the role of modules of molecules as opposed to individual proteins acting in isolation; (3) it enables discovery of novel emergent properties; (4) it demonstrates the importance of networks in biology; and (5) it adds new dimensionality to the study of biological systems.

Cardiac proteomic responses to ischemia-reperfusion injury and ischemic preconditioning

Cardiac ischemia and ischemia-reperfusion (I/R) injury are major contributors to morbidity and mortality worldwide. Pathological mechanisms of I/R and the physiological mechanisms of ischemic preconditioning (IPC), which is an effective cardiac protective response, have been widely investigated in the last decade to search for means to prevent or treat this disease. Proteomics is a powerful analytical tool that has provided important information to identify target proteins and understand the underlying mechanisms of I/R and IPC. Here, we review the application of proteomics to I/R injury and IPC to discover target proteins. We analyze the functional meaning of the accumulated data on hundreds of proteins using various bioinformatics applications. In addition, we review exercise-induced proteomic alterations in the heart to understand the potential cardioprotective role of exercise against I/R injury. Further developments in the proteomic field that target specialized proteins will yield new insights for optimizing therapeutic targets and developing a wide range of therapeutic agents against ischemic heart disease.

Connexin43 phosphorylation and cytoprotection in the heart

The fundamental role played by connexins including connexin43 (Cx43) in forming intercellular communication channels (gap junctions), ensuring electrical and metabolic coupling between cells, has long been recognized and extensively investigated. There is also increasing recognition that Cx43, and other connexins, have additional roles, such as the ability to regulate cell proliferation, migration, and cytoprotection. Multiple phosphorylation sites, targets of different signaling pathways, are present at the regulatory, C-terminal domain of Cx43, and contribute to constitutive as well as transient phosphorylation Cx43 patterns, responding to ever-changing environmental stimuli and corresponding cellular needs. The present paper will focus on Cx43 in the heart, and provide an overview of the emerging recognition of a relationship between Cx43, its phosphorylation pattern, and development of resistance to injury. We will also review our recent work regarding the role of an enhanced phosphorylation state of Cx43 in cardioprotection. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.

Enhanced protection against pulmonary hypertension with sildenafil and endothelial progenitor cell in rats

BACKGROUND

Sildenafil and bone marrow-derived endothelial progenitor cells (BMDEPCs) have been shown to ameliorate monocrotaline (MCT)-induced pulmonary arterial hypertension (PAH) in the rat. We test whether combined sildenafil and BMDEPC treatment exerts additional protection against MCT-induced PAH in rats.

METHODS

Male Sprague-Dawley rats were randomized to receive saline injection only (group 1), MCT (70 mg/kg) only (group 2), MCT plus autologous BMDEPC (2.0×10(6) cells) transplantation (group 3), MCT with sildenafil (30 mg/kg/day) (group 4), and MCT with combined BMDEPCs-sildenafil (30 mg/kg/day) (group 5). Intravenous BMDEPC and oral sildenafil were given on day 3 after MCT administration. Hemodynamics were analyzed using Labchart software, whereas cellular and molecular parameters were measured using flow cytometry, real-time PCR, TUNEL assay, Western blot, and immunohistochemical staining.

RESULTS

By day 35 following MCT treatment, lower expression of connexin43, protein kinase C-ε, Bcl-2, and endothelial nitric oxide synthase and higher expression of tumor necrosis factor-α and caspase 3 were found in right ventricle (RV) and lung in group 2 compared with other groups (all p<0.05). The number of alveolar sacs and lung arterioles were also lower in group 2 than in other groups (all p<0.05). Furthermore, RV systolic pressure (RVSP), RV weight, and RV-to-final body weight ratio were substantially increased in group 2 than in other groups, and notably higher in groups 3 and 4 than in groups 1 and 5 (all p<0.0001).

CONCLUSIONS

Combined therapy with autologous BMDEPC and sildenafil is superior to either BMDPEC or sildenafil alone for preventing MCT-induced PAH.

Impact of hyperglycemic control on left ventricular myocardium. A molecular and cellular basic study in a diabetic rat model

This experimental study investigated the impact of hyperglycemic control on left ventricular (LV) function using a model of diabetes mellitus (DM) (induced by streptozocin 60 mg/kg). Sixteen adult-Sprague Dawley rats were divided into group 1 (poor hyperglycemic control, n = 8) and group 2 (good hyperglycemic control, n = 8). Diabetic rats and 8 healthy rats serving as controls (group 3) were sacrificed on day 28 after DM induction. The results demonstrated that HbA(1C) on day 28 was higher in group 1 than in groups 2 and 3 (P < 0.0001). The mRNA expressions of MMP-9 and endothelin-1 were elevated in group 1 compared with that in groups 2 and 3 (P < 0.05), whereas PGC-1alpha and eNOS were lower in group 1 than in groups 2 and 3 (P < 0.05). The number of apoptotic nuclei was higher in group 1 than in groups 2 and 3 (P < 0.01). The integrated area (microm(2)) of connexin43 (Cx43), Cx43 protein expression, and LV function were lower in group 1 than in groups 2 and 3 (P < 0.05). Moreover, PKC-epsilon expression in the mitochondrial compartment was decreased in group 1 compared to that in groups 2 and 3 (P < 0.005).

Proteomics of the heart: unraveling disease

Heart diseases resulting in heart failure are among the leading causes of morbidity and mortality in developed countries. Underlying molecular causes of cardiac dysfunction in most heart diseases are still largely unknown but are expected to result from causal alterations in gene and protein expression. Proteomic technology now allows us to examine global alterations in protein expression in the diseased heart and can provide new insights into cellular mechanisms involved in cardiac dysfunction. The majority of proteomic investigations still use 2D gel electrophoresis (2-DE) with immobilized pH gradients to separate the proteins in a sample and combine this with mass spectrometry (MS) technologies to identify proteins. In spite of the development of novel gel-free technologies, 2-DE remains the only technique that can be routinely applied to parallel quantitative expression profiling of large sets of complex protein mixtures such as whole cell lysates. It can resolve >5000 proteins simultaneously (approximately 2000 proteins routinely) and can detect <1 ng of protein per spot. Furthermore, 2-DE delivers a map of intact proteins, which reflects changes in protein expression level, isoforms, or post-translational modifications. The use of proteomics to investigate heart disease should result in the generation of new diagnostic and therapeutic markers. In this article, we review the current status of proteomic technologies, describing the 2-DE proteomics workflow, with an overview of protein identification by MS and how these technologies are being applied to studies of human heart disease.

Fibroblast growth factor-2 and cardioprotection

Boosting myocardial resistance to acute as well as chronic ischemic damage would ameliorate the detrimental effects of numerous cardiac pathologies and reduce the probability of transition to heart failure. Experimental cardiology has pointed to ischemic and pharmacological pre- as well as post-conditioning as potent acute cardioprotective manipulations. Additional exciting experimental strategies include the induction of true regenerative and/or angiogenic responses to the damaged heart, resulting in sustained structural and functional beneficial effects. Fibroblast growth factor-2 (FGF-2), an endogenous multifunctional protein with strong affinity for the extracellular matrix and basal lamina and well-documented paracrine, autocrine and intracellular modes of action, has been shown over the years to exert acute and direct pro-survival effects, irrespectively of whether it is administered before, during or after an ischemic insult to the heart. FGF-2 is also a potent angiogenic protein and a crucial agent for the proliferation, expansion, and survival of several cell types including those with stem cell properties. Human clinical trials have pointed to a good safety record for this protein. In this review, we will present a case for the low molecular weight isoform of fibroblast growth factor-2 (lo-FGF-2) as a very promising therapeutic agent to achieve powerful acute as well as sustained benefits for the heart, due to its cytoprotective and regenerative properties.

Proteomic analysis of pharmacological preconditioning: novel protein targets converge to mitochondrial metabolism pathways

Ischemic preconditioning is characterized by resistance to ischemia reperfusion injury in response to previous short ischemic episodes, a protective effect that can be mimicked pharmacologically. The underlying mechanism of protection remains controversial and requires greater understanding before it can be fully exploited therapeutically. To investigate the overall effect of preconditioning on the myocardial proteome, isolated rabbit ventricular myocytes were treated with drugs known to induce preconditioning, adenosine or diazoxide (each at 100 micromol/L for 60 minutes). Their protein profiles were then compared with vehicle-treated controls (n=4 animals per treatment) using a multitiered 2D gel electrophoresis approach. Of 28 significantly altered protein spots, 19 nonredundant proteins were identified (5 spots remained unidentified). The majority of these proteins are involved in mitochondrial energetics, including subunits of tricarboxylic acid cycle enzymes and oxidative phosphorylation complexes. These changes were not indiscriminate, with only a small number of enzymes or complex subunits altered, indicating a very specific and targeted affect of these 2 preconditioning mimetics. Among the changes were shifts in the extent of posttranslational modification of 4 proteins. One of these, the adenosine-induced phosphorylation of the ATP synthase beta subunit, was fully characterized with the identification of 5 novel phosphorylation sites. This proteomics approach provides an overall assessment of the cellular response to pharmacological treatment with adenosine and diazoxide and identifies a distinct subset of enzymes and protein complex subunit that may underlie the preconditioned phenotype.

The therapeutic potential of monoamine oxidase inhibitors

Monoamine oxidase inhibitors were among the first antidepressants to be discovered and have long been used as such. It now seems that many of these agents might have therapeutic value in several common neurodegenerative conditions, independently of their inhibition of monoamine oxidase activity. However, many claims and some counter-claims have been made about the physiological importance of these enzymes and the potential of their inhibitors. We evaluate these arguments in the light of what we know, and still have to learn, of the structure, function and genetics of the monoamine oxidases and the disparate actions of their inhibitors.

Mitochondria and ischemia/reperfusion injury

Cardiac ischemia/reperfusion injury results in a variable mixture of apoptotic, necrotic, and normal tissue that depends on both the duration and severity of ischemia. Injury can be abrogated by activation of protective pathways via ischemic and pharmacologic preconditioning. Mitochondria serve as final arbiters of life and death of the cell as these organelles not only are required to generate ATP but also can trigger apoptosis or necrosis. A key mechanism of mitochondrial injury is by the mitochondrial permeability transition (MPT) that has been shown to occur at reperfusion. The article hypothesizes that ischemia/reperfusion promotes MPT in two phases: (1) MPT priming during ischemia occurs as progressive inner mitochondrial membrane leak is accompanied by depressed electron transport in the setting of fatty acid accumulation and loss of cytochrome c and antioxidants; and (2) Triggering of MPT at reperfusion is determined by the interplay of mitochondrial membrane potential (DeltaPsi(m)) with mitochondrial matrix Ca, reactive oxygen species, and pH. It has been found that strategies that promote mitochondrial recovery such as pharmacologic preconditioning by diazoxide are mediated by K(+)-dependent regulation of matrix volume and DeltaPsi(m), resulting in improved efficiency of ATP synthesis as well as prevention of cytochrome c loss. If mitochondria fail to recover, then MPT and hypercontracture can result as DeltaPsi(m) depolarization waves regeneratively cross the cell (0.1 to 0.2 microm/s).

PKC-induced ERK1/2 interactions and downstream effectors in ovine cerebral arteries

Both protein kinase C (PKC) and extracellular signal-regulated kinases (ERK1/2) are involved in mediating vascular smooth muscle contraction. We tested the hypotheses that in addition to PKC activation of ERK1/2, by negative feedback ERKs modulate PKC-induced contraction, and that their interactions modulate both thick and thin myofilament pathways. In ovine middle cerebral arteries (MCA), we measured isometric tension and intracellular free calcium concentration ([Ca(2+)](i)) responses to PKC stimulation [phorbol 12,13-dibutyrate (PDBu), 3 x 10(-6) M] in the absence or presence of ERK1/2 inhibition (U-0126, 10(-5) M). After PDBu +/- ERK1/2 inhibition, we also examined by Western immunoblot the levels of total and phosphorylated ERK1/2, caldesmon(Ser789), myosin light chain(20) (MLC(20)), and CPI-17. PDBu induced significant increase in tension in the absence of increased [Ca(2+)](i). PDBu also increased phosphorylated ERK1/2 levels, a response blocked by U-0126. In turn, U-0126 augmented PDBu-induced contractions. PDBu also was associated with significant increases in phosphorylated caldesmon(Ser789) and MLC(20) levels, each of which peaked at 5 to 10 min. PDBu also increased phosphorylated CPI-17 levels, which peaked at 2 to 3 min. Rho kinase inhibition (Y-27632, 3 x 10(-7) M) did not alter PDBu-induced contraction. These results support the idea that PKC activation can increase CPI-17 phosphorylation to decrease myosin light chain phosphatase activity. In turn, this increases MLC(20) phosphorylation in the thick filament pathway and increases Ca(2+) sensitivity. In addition, ERK1/2-dependent phosphorylation of caldesmon(Ser789) was not necessary for PDBu-induced contraction and appears not to be involved in the reversal of caldesmon's inhibitory effect on actin-myosin ATPase.

Age- and sex-dependent alterations in protein kinase C (PKC) and extracellular regulated kinase 1/2 (ERK1/2) in rat myocardium

Cardiovascular morbidity and mortality increase significantly with advancing age, with proportionally higher rates occurring in aged women when compared to aged men. The signaling alterations responsible for age-related reductions in ischemic stress reserves, particularly in aged women, are poorly understood. Accordingly, we sought to determine whether alterations in the cellular location and formation of specific protein kinase C (PKC)-extracellular regulated 1/2 (ERK1/2) signaling modules (SMS) might provide insight into known age- and sex-related differences in cardiovascular disease outcomes. Cytosolic (Cyto), mitochondrial (Mito) and nuclear (Nuc) fractions were isolated from left ventricles of male (M) and female (F) adult (6 mo), castrated or aged (23 mo) F344 rats by centrifugation. Western blotting was used to assess PKC (alpha, delta, epsilon), p-ERK1/2 and p-Bad(Ser112) levels, and immunoprecipitation to assess PKC-ERK1/2 SMS. Cyto-PKCalpha levels increased with age (p<0.0001), whereas increases in cyto-PKCalpha-ERK1/2 SMS were only observed in aged F (60%; p<0.01). Mito-PKCdelta and Mito-PKCdelta-ERK1/2 SMS increased in M and F with age (p<0.0001); however increases in Cyto-PKCdelta were only observed in aged M (80% p<0.0001). It is important to note that Nuc- and Mito-PKCdelta-ERK1/2 SMS were 3.5- and 4.8-fold greater in males versus females, respectively (p<0001). Increases in Mito-PKCepsilon-ERK1/2 SMS (216%) were also specific to aged M (p<0.0001), however, Mito-p-Bad(Ser112) levels were decreased with age in both M and F. Differences in sex hormone status could not fully account for observed age-related differences in PKC. Collectively, our results provide novel evidence for age and sex-related differences in the magnitude and distribution of cardiac PKC-ERK1/2 SMS consistent with previously described pathological and protective phenotypes, respectively.

Functional proteomic analysis of a three-tier PKCepsilon-Akt-eNOS signaling module in cardiac protection

Cardiac protective signaling networks have been shown to involve PKCepsilon. However, the molecular mechanisms by which PKCepsilon interacts with other members of these networks to form task-specific modules remain unknown. Among 93 different PKCepsilon-associated proteins that have been identified, Akt and endothelial nitric oxide (NO) synthase (eNOS) are of importance because of their independent abilities to promote cell survival and prevent cell death. The simultaneous association of PKCepsilon, Akt, and eNOS has not been examined, and, in particular, the formation of a module containing these three proteins and the role of such a module in the regulation of NO production and cardiac protection are unknown. The present study was undertaken to determine whether these molecules form a signaling module and, thereby, play a collective role in cardiac signaling. Using recombinant proteins in vitro and PKCepsilon transgenic mouse hearts, we demonstrate the following: 1) PKCepsilon, Akt, and eNOS interact and form signaling modules in vitro and in the mouse heart. Activation of either PKCepsilon or Akt enhances the formation of PKCepsilon-Akt-eNOS signaling modules. 2) PKCepsilon directly phosphorylates and enhances activation of Akt in vitro, and PKCepsilon activation increases phosphorylation and activation of Akt in PKCepsilon transgenic mouse hearts. 3) PKCepsilon directly phosphorylates eNOS in vitro, and this phosphorylation enhances eNOS activity. Activation of PKCepsilon in vivo increased phosphorylation of eNOS at Ser(1177), indicating eNOS activation. This study characterizes, for the first time, the physical, as well as functional, coupling of PKCepsilon, Akt, and eNOS in the heart and implicates these PKCepsilon-Akt-eNOS signaling modules as critical signaling elements during PKCepsilon-induced cardiac protection.

Chronic Exercise Improves Myocardial Inotropic Reserve Capacity Through α1-Adrenergic and Protein Kinase C-Dependent Effects in Senescent Rats

We have previously demonstrated that α1-adrenergic (AR)-mediated contraction is diminished in the senescent rat heart, in part due to alterations in protein kinase C (PKC) signaling. Since chronic exercise training (EX) can exert independent effects on increasing α1-AR contraction in the adult rat heart, we sought to determine whether age-related defects in α1-AR contraction could be reversed by chronic EX. We further hypothesized that improved α1-AR contraction by EX may be PKC dependent. Adult (4 months; Y) and aged (24 months; O) male F344 rats were treadmill-trained (n = 12–13/group; TR) at ∼70% of VO2max for 12 weeks or remained sedentary (YSED, YTR, OSED, OTR). Training status was verified by plantaris citrate synthase activity and left ventricular (LV) contractile responses (dP/dt) to α1-AR stimulation were assessed in Langendorff-perfused hearts using the α1-AR agonist phenylephrine (PE; 10−5 M) with and without the PKC inhibitor chelerythrine (CE; 10−6 M). α1-AR stimulation elicited greater increases in LV dP/dt in hearts isolated from OTR (4525.4 ± 224.1 mmHg/s) versus OSED (3658.9 ± 291.0 mmHg/s), while CE abolished PE-induced effects (OTR, 4069.2 ± 341.2) versus (OSED, 3608.9 ± 321.2) (p &lt;.01). Upon western blotting, phosphospecific antibodies directed at PKCε (pSer729) revealed greater levels in LV isolated from YTR versus YSED, and EX ameliorated aged-related reductions in OSED (p &lt;.001). Basal PKCε mRNA levels were also greater in YTR and OTR versus YSED (p &lt;.01). PE-induced increases in phosphor-PKCδ (pThr507) levels observed in OSED were attenuated in OTR (p &lt;.03). Chronic EX was also associated with significant reductions in PKCα (pSer657) levels following PE in OTR (p &lt;.002). The results indicate that age-related reductions in α1-AR contraction can be partially reversed by EX in the rat heart. These results further suggest that alterations in PKC levels underlie, at least in part, EX-induced improvements in α1-AR contraction.

Opposing roles of δ and εPKC in cardiac ischemia and reperfusion: targeting the apoptotic machinery

Heart attacks, or acute myocardial infarctions (AMI), affect more than one million people in the US every year. The damage that occurs to the heart by AMI is often permanent and as a result, the morbidity and mortality rates of patients that experience AMIs continue to be high. Consequently, AMI patients are at significantly increased risks for future myocardial infarctions, decreased heart function, heart failure, and death [Heart and Stroke statistical update. In American Heart Association (2002) 4]. In this review, we discuss the events that lead to cardiac damage by AMI. Specifically, we discuss the current understanding of the role of ischemic damage vs. reperfusion damage, which is induced by the return of blood, oxygen, and nutrients to the organ. We also discuss the role of apoptosis and necrosis in cardiac damage, the means to protect the heart from damage by ischemia and reperfusion, and the role of protein kinase C in these processes.

Identification of Novel Signaling Complexes by Functional Proteomics

The rapid development of proteomic technologies, combined with the completion of the Human Genome Map, has enabled the compiling of an unprecedented inventory of cellular proteins. Functional proteomics is an emerging field that aims to utilize the enormous amount of information provided by these proteomic technologies to understand the functions of cellular proteins. The utility of functional proteomics has been recently exploited to elucidate cellular mechanisms in numerous fields, of particular salience in the area of signal transduction. This review presents a functional proteomic approach for the study of cardiac cell signaling. It illustrates the strategies by which the subproteome of a targeted signaling system is characterized in an unbiased fashion, the manner in which the biochemical functions of this subproteome are assessed using established molecular and protein chemistry methods, and the challenges associated with these studies.

Role of the mitochondrial permeability transition in myocardial disease

Mitochondria play a key role in determining cell fate during exposure to stress. Their role during ischemia/reperfusion is particularly critical because of the conditions that promote both apoptosis by the mitochondrial pathway and necrosis by irreversible damage to mitochondria in association with mitochondrial permeability transition (MPT). MPT is caused by the opening of permeability transition pores in the inner mitochondrial membrane, leading to matrix swelling, outer membrane rupture, release of apoptotic signaling molecules such as cytochrome c from the intermembrane space, and irreversible injury to the mitochondria. During ischemia (the MPT priming phase), factors such as intracellular Ca2+ accumulation, long-chain fatty acid accumulation, and reactive oxygen species progressively increase mitochondrial susceptibility to MPT, increasing the likelihood that MPT will occur on reperfusion (the MPT trigger phase). Because functional cardiac recovery ultimately depends on mitochondrial recovery, cardioprotection by ischemic and pharmacological preconditioning must ultimately involve the prevention of MPT. Investigations into this area are beginning to unravel some of the mechanistic links between cardioprotective signaling and mitochondria.

Ischemic preconditioning preserves connexin 43 phosphorylation during sustained ischemia in pig hearts in vivo

During myocardial ischemia, connexin 43 (Cx43) is dephosphorylated in vitro, and the subsequent opening of gap junctions formed by two opposing Cx43 hexamers was suggested to propagate ischemia/reperfusion injury. Reduction of infarct size (IS) by ischemic preconditioning (IP) involves activation of protein kinase C (PKC) and p38 mitogen activated protein kinase (MAPK), both of which can phosphorylate Cx43. We now studied in anesthetized pigs whether IP impacts on Cx43 phosphorylation by measuring the density of non-phosphorylated and total Cx43 (confocal laser) during normoperfusion and 90-min ischemia in non-preconditioned and preconditioned hearts. Co-localization of PKCalpha, p38MAPKalpha, and p38MAPKbeta with Cx43 and the activity of p38MAPK were assessed. IP by 10 min ischemia and 15 min reperfusion reduced IS. Non-phosphorylated Cx43 remained unchanged during ischemia in preconditioned hearts, while it increased from 35+/-3 to 75+/-8 AU (P<0.05) in non-preconditioned hearts. Co-localization of PKCalpha, p38MAPKalpha, and p38MAPKbeta with Cx43 during ischemia increased only in preconditioned hearts. While the ischemia-induced increase in p38MAPKalpha activity was comparable in preconditioned and non-preconditioned hearts, p38MAPKbeta activity was increased only in preconditioned hearts. Blockade of p38MAPK by SB203580 attenuated the IS-reduction and the increased p38MAPK-Cx43 co-localization by IP. We conclude that IP increases co-localization of protein kinases with Cx43 and preserves phosphorylation of Cx43 during ischemia.

Genome informatics: current status and future prospects

This article reviews recent advances in genomics and informatics relevant to cardiovascular research. In particular, we review the status of (1) whole genome sequencing efforts in human, mouse, rat, zebrafish, and dog; (2) the development of data mining and analysis tools; (3) the launching of the National Heart, Lung, and Blood Institute Programs for Genomics Applications and Proteomics Initiative; (4) efforts to characterize the cardiac transcriptome and proteome; and (5) the current status of computational modeling of the cardiac myocyte. In each instance, we provide links to relevant sources of information on the World Wide Web and critical appraisals of the promises and the challenges of an expanding and diverse information landscape.

[Proteomics and cardiovascular disease]

The description of the human genome has opened new venues for the study and understanding of pathophysiological phenomena. In the 20th century, individual cell components were studied. The 21st century began with a global analysis of cell components. Thanks to the development of new technologies such as DNA chips, or two-dimensional electrophoresis, we can now study the expression of thousands of genes, or the proteins they encode, in a few hours. Genomics has opened the way for proteomics. Improved knowledge of genes does not provide information about cell functions, because any cell expresses all genes simultaneously. Instead, there is selective gene expression depending on the cell type and the stimuli to which it is exposed. The result of this is the proteome, an ensemble of proteins that are responsible for cell functions at any given moment, which are the object of the study of proteomics. The description of the proteome of cardiac cells has begun and some new proteins have been found to be dysregulated in different cardiomyopathies. These proteins are involved either in energy production or in the stress response, or belong to the cell proteasome or cytoskeleton. They may be potential risk markers or new therapeutic targets in the future. In this sense, chemogenomics is a new methodology for the development of new drugs using genomic and proteomic data.

No ischemic preconditioning in heterozygous connexin43-deficient mice

Protein kinase Cepsilon (PKCepsilon) plays a central role in ischemic preconditioning (IP) in mice and rabbits, and activated PKCepsilon colocalizes with and phosphorylates connexin43 (Cx43) in rats and humans. Whether or not Cx43 contributes to the mechanism(s) of IP in vivo is yet unknown. Therefore, wild-type (n = 8) and heterozygous Cx43-deficient mice (n = 8) were subjected to 30 min occlusion and 120 min reperfusion of the left anterior descending coronary artery. IP was induced by one cycle of 5 min occlusion and 10 min reperfusion (n = 8/8 mice) before the sustained occlusion. Infarct size was reduced by IP in wild-type mice [11.3 +/- 3.4% vs. 23.7 +/- 7.2% of the left ventricle (LV), P < 0.05] but not in Cx43-deficient mice (26.0 +/- 6.0% vs. 25.1 +/- 3.8% of LV). Also, three cycles of 5 min occlusion and 10 min reperfusion (n = 5) did not induce protection in Cx43-deficient mice (27.6 +/- 5.5 % of LV). Thus Cx43 contributes to the protection of IP in mice in vivo.

Moderate alcohol consumption induces sustained cardiac protection by activating PKC-epsilon and Akt

C57BL/6 mice were fed 18% ethanol (vol/vol) in drinking water for 12 wk. Isovolumic hearts were subjected to 20 min of ischemia and 30 min of reperfusion on a Langendorff apparatus. There were no differences in baseline hemodynamic function between hearts from ethanol (EtOH)-fed mice and controls. However, prior alcohol consumption doubled recovery of left ventricular developed pressure (68 +/- 8 vs. 33 +/- 8 mmHg for controls; n = 10, P < 0.05) and reduced creatine kinase release by half (0.26 +/- 0.04 vs. 0.51 +/- 0.08 U x min(-1) x g wet wt(-1) for controls; n = 10, P < 0.05). EtOH feeding doubled expression of activated protein kinase C epsilon (PKC)epsilon (n = 6, P < 0.05); whereas PKC inhibition blocked protection during ischemia-reperfusion. EtOH feeding also increased expression of Akt three- to fivefold (n = 6, P < 0.05), whereas PKC inhibition prevented increases in Akt kinase activity. We conclude that signaling pathways involving PKC-epsilon are critical for sustained EtOH-mediated cardioprotection and that Akt may be a downstream effector of resistance to myocardial reperfusion injury.

Separation and identification of human heart proteins

Heart failure is not a uniform disease entity, but a syndrome with various causes, including hypertension, ischemia and congenital heart disease, cardiomyopathy, myocarditis and intoxication. During the recent years a number of molecular and cellular alterations have been identified in the diseased heart, but a direct causative link between these changes and functional impairment, medical responsiveness, progression of the disease and the patients' outcome remains to be established. After an accumulation of large amounts of DNA sequence data in genomic projects, scientists have now turned their attention to the central executors of all programs of life, the proteins. In complementation of the genomic initiatives, proteomics based approaches have lined up not only for large-scale identification of proteins and their post-translational modifications, but also to study the function of protein complexes, protein-protein interactions and regulatory and signalling cascades in the cellular network. In concert with genomic data functional proteomics will hold the key for a better understanding and therapeutical management of cardiovascular diseases in the future.

Mitochondrial PKCepsilon and MAPK form signaling modules in the murine heart: enhanced mitochondrial PKCepsilon-MAPK interactions and differential MAPK activation in PKCepsilon-induced cardioprotection

Although activation of protein kinase C (PKC) epsilon and mitogen-activated protein kinases (MAPKs) are known to play crucial roles in the manifestation of cardioprotection, the spatial organization of PKCepsilon signaling modules in naïve and protected myocardium remains unknown. Based on evidence that mitochondria are key mediators of the cardioprotective signal, we hypothesized that PKCepsilon and MAPKs interact, and that they form functional signaling modules in mitochondria during cardioprotection. Both immunoblotting and immunofluorescent staining demonstrated that PKCepsilon, ERKs, JNKs, and p38 MAPK co-localized with cardiac mitochondria. Moreover, transgenic activation of PKCepsilon greatly increased mitochondrial PKCepsilon expression and activity, which was concomitant with increased mitochondrial interaction of PKCepsilon with ERKs, JNKs, and p38 as determined by co-immunoprecipitation. These complex formations appeared to be independent of PKCepsilon activity, as the interactions were also observed in mice expressing inactive PKCepsilon. However, although both active and inactive PKCepsilon bound to all three MAPKs, increased phosphorylation of mitochondrial ERKs was only observed in mice expressing active PKCepsilon but not in mice expressing inactive PKCepsilon. Examination of potential downstream targets of mitochondrial PKCepsilon-ERK signaling modules revealed that phosphorylation of the pro-apoptotic protein Bad was elevated in mitochondria. Together, these data show that PKCepsilon forms subcellular-targeted signaling modules with ERKs, leading to the activation of mitochondrial ERKs. Furthermore, formation of mitochondrial PKCepsilon-ERK modules appears to play a role in PKCepsilon-mediated cardioprotection, in part by the phosphorylation and inactivation of Bad.

Molecular conformation dictates signaling module formation: example of PKCepsilon and Src tyrosine kinase

Our laboratory has conducted multiple functional proteomic analyses to characterize the components of protein kinase C (PKC)epsilon cardioprotective signaling complexes and found that activation of PKCepsilon induces dynamic modulation of these complexes. In addition, it is known that signal transduction within a complex involves the formation of modules, one of which has been shown to include PKCepsilon and Src tyrosine kinase in the rabbit heart. However, the cellular mechanisms that define the assembly of PKCepsilon modules remain largely unknown. To address this issue, the interactions between PKCepsilon and Src were studied. We used recombinant proteins of wild-type PKCepsilon (PKCepsilon-WT) and open conformation mutants of the kinase (PKCepsilon-AE5 and PKCepsilon-AN59), the regulatory and catalytic domains of PKCepsilon, along with glutathione-S-transferase (GST) fusion proteins of Src (GST-Src) and two domains of Src (GST-SH2 and GST-SH3). GST pulldown assays demonstrated that Src and PKCepsilon are binding partners and that the interaction between PKCepsilon and Src appears to involve multiple sites. This finding was supported for endogenous PKCepsilon and Src in the murine heart using immunofluorescence-based confocal microscopy and coimmunoprecipitation. Furthermore, PKCepsilon-WT and GST-Src interactions were significantly enhanced in the presence of phosphatidyl-L-serine, an activator of PKC, indicating that Src favors interaction with activated PKCepsilon. This finding was confirmed when the PKCepsilon-WT was replaced with PKCepsilon-AE5 or PKCepsilon-AN59, demonstrating that the conformation of PKCepsilon is a critical determinant of its interactions with Src. Together, these results illustrate that formation of a signaling module between PKCepsilon and Src involves specific domains within the two molecules and is governed by the molecular conformation of PKCepsilon.

Formation of protein kinase C(epsilon)-Lck signaling modules confers cardioprotection

The epsilon isoform of protein kinase C (PKCepsilon) is a member of the PKC family of serine/threonine kinases and plays a critical role in protection against ischemic injury in multiple organs. Functional proteomic analyses of PKCepsilon signaling show that this isozyme forms multiprotein complexes in the heart; however, the precise signaling mechanisms whereby PKCepsilon orchestrates cardioprotection are poorly understood. Here we report that Lck, a member of the Src family of tyrosine kinases, forms a functional signaling module with PKCepsilon. In cardiac cells, PKCepsilon interacts with, phosphorylates, and activates Lck. In vivo studies showed that cardioprotection elicited either by cardiac-specific transgenic activation of PKCepsilon or by ischemic preconditioning enhances the formation of PKCepsilon-Lck modules. Disruption of these modules, via ablation of the Lck gene, abrogated the infarct-sparing effects of these two forms of cardioprotection, indicating that the formation of PKCepsilon-Lck signaling modules is required for the manifestation of a cardioprotective phenotype. These findings demonstrate, for the first time to our knowledge, that the assembly of a module (PKCepsilon-Lck) is an obligatory step in the signal transduction that results in a specific phenotype. Thus, PKCepsilon-Lck modules may serve as novel therapeutic targets for the prevention of ischemic injury.

Enhanced PKC beta II translocation and PKC beta II-RACK1 interactions in PKC epsilon-induced heart failure: a role for RACK1

Recent investigations have established a role for the beta II-isoform of protein kinase C (PKC beta II) in the induction of cardiac hypertrophy and failure. Although receptors for activated C kinase (RACKs) have been shown to direct PKC signal transduction, the mechanism through which RACK1, a selective PKC beta II RACK, participates in PKC beta II-mediated cardiac hypertrophy and failure remains undefined. We have previously reported that PKC epsilon activation modulates the expression of RACKs, and that altered epsilon-isoform of PKC (PKC epsilon)-RACK interactions may facilitate the genesis of cardiac phenotypes in mice. Here, we present evidence that high levels of PKC epsilon activity are commensurate with impaired left ventricular function (dP/dt = 6,074 +/- 248 mmHg/s in control vs. 3,784 +/- 269 mmHg/s in transgenic) and significant myocardial hypertrophy. More importantly, we demonstrate that high levels of PKC epsilon activation induce a significant colocalization of PKC beta II with RACK1 (154 +/- 7% of control) and a marked redistribution of PKC beta II to the particulate fraction (17 +/- 2% of total PKC beta II in control mice vs. 49 +/- 5% of total PKC beta II in hypertrophied mice), without compensatory changes of the other eight PKC isoforms present in the mouse heart. This enhanced PKC beta II activation is coupled with increased RACK1 expression and PKC beta II-RACK1 interactions, demonstrating PKC epsilon-induced PKC beta II signaling via a RACK1-dependent mechanism. Taken together with our previous findings regarding enhanced RACK1 expression and PKC epsilon-RACK1 interactions in the setting of cardiac hypertrophy and failure, these results suggest that RACK1 serves as a nexus for at least two isoforms of PKC, the epsilon-isoform and the beta II-isoform, thus coordinating PKC-mediated hypertrophic signaling.

Protein kinase C epsilon-Src modules direct signal transduction in nitric oxide-induced cardioprotection: complex formation as a means for cardioprotective signaling

An essential role for protein kinase C epsilon (PKCepsilon) has been shown in multiple forms of cardioprotection; however, there is a distinct paucity of information concerning the signaling architecture that is responsible for the manifestation of a protective phenotype. We and others have recently shown that signal transduction may proceed via the formation of signaling complexes (Circ Res. 2001;88:59-62). In order to understand if the assembly of multiprotein complexes is the manner by which signaling is conducted in cardioprotection, we designed a series of experiments to characterize the associations of Src tyrosine kinase with PKCepsilon in a conscious rabbit model of nitric oxide (NO)-induced late preconditioning. Our data demonstrate that PKCepsilon and Src can form functional signaling modules in vitro: PKCepsilon interacts with Src; the association with PKCepsilon activates Src; and adult cardiac cells receiving recombinant adenoviruses encoding PKCepsilon exhibit increased Src activity. Furthermore, our results show that NO-induced late preconditioning involved PKCepsilon-Src module formation and enhanced the enzymatic activity of PKCepsilon-associated Src. Inhibition of PKC blocked cardioprotection, module formation, and PKCepsilon-associated Src activity, providing direct evidence for a functional role of the PKCepsilon-Src module in the orchestration of NO-induced cardioprotection in conscious rabbits.